Heretofore, there have been known driving force transmission devices for hybrid vehicle which include a rotation shaft for transmitting a rotational driving force to the driving wheels, and the engine and motor for driving the rotation shaft. Some of the driving force transmission devices are equipped with the auxiliary device driving mechanism for driving the in-vehicle auxiliary device such as the oil pump with the driving force of the engine or motor.
As an example of the auxiliary device driving mechanism, a driving mechanism for vehicle oil pump is set forth in patent document 1. This driving mechanism includes a first power transmission path interconnecting an output shaft of the motor and a drive shaft of the oil pump, and a second power transmission path interconnecting an output shaft of the engine and the drive shaft of the oil pump. The first power transmission path is provided with a first one-way clutch permitting only power transmission from the motor to the oil pump while the second power transmission path is provided with a second one-way clutch permitting only power transmission from the engine to the oil pump. With the engine and the motor simultaneously driven, this structure is adapted to drive the oil pump by way of either one of the engine and the motor that provides the greater rotational driving force.
The driving mechanism for vehicle oil pump disclosed in the patent document 1 is applicable to a case where the engine and the motor are rotatable only in normal direction. Therefore, this mechanism has a problem that when a vehicle is at a stop with its engine turned off, both of the power sources, namely the engine and the motor, are shut down and hence, the vehicle cannot maintain a required hydraulic pressure. The problem dictates the need to provide the oil pump, such as an electric oil pump, that is driven by a separate driving unit. This may result in the increase in the number of components, costs and weight.
An arrangement in which the auxiliary devices are driven by a driving motor is set forth in patent document 2. However, the auxiliary device driving mechanism disclosed in the patent document 2 has the following problem. When the vehicle is at a stop, a clutch between a gearbox and the motor must be disengaged to permit the auxiliary device to be driven. To restart the vehicle, on the other hand, a procedure starting from the shut-down motor followed by engaging the clutch and activating the motor need be performed. This results in the occurrence of time lag, which may reduce the merchantability of the vehicle in terms of startability. Further in a case where the clutch is used as the mechanism for disconnecting the power transmission between the gearbox and the motor, high production costs result because the clutch and components of a control system thereof are necessary.
A drive mechanism for an oil pump having inputs from two systems of the engine and an electric motor is set forth in patent document 3. In order to allow the motor to operate in reverse rotation, this drive mechanism adopts an oil passage switching structure employing a reversible pump and a cross valve. However, this drive mechanism involves a fear of complicated vehicle structure and increased weight and cost because the reversible pump and the associated electric devices are added to make the oil passage structure more complicated. Furthermore, the reversible pump has a lower efficiency than a one-way pump and thence may result in reduced fuel economy. Therefore, this drive mechanism is not adequate to improve the energy efficiency of the vehicle.